Question 14
A table comparing the properties of polycarbonate (PC) and acrylonitrile butadiene styrene (ABS) is shown.
| Properties | Polycarbonate (PC) | Acrylonitrile butadiene styrene (ABS) |
|---|---|---|
| Mechanical | very high impact resistance; tough; rigid; good dimensional stability | high impact resistance; tough; hard; rigid; lightweight |
| Impact strength (notched Izod) | 600–850 J/m | 200–300 J/m |
| Optical | transparent | opaque; takes colour and gloss finishes well |
| Light transmission (3 mm sheet) | 88–90% | 0% |
| Maximum service temperature | 115–130 °C | 80–90 °C |
| Chemical | good resistance to water and dilute acids; attacked by petrol and many solvents | good resistance to water, acids and alkalis; attacked by some solvents |
| Manufacturing cost | moderate | low |
Analyse the information in the table to determine whether PC or ABS is the most suitable material for the visor of a motorcycle helmet. Justify your response with four properties from the table.
Light, a stone and the sun: three tests the table answers
Each beat tests the visor one property at a time and compares the PC and ABS values from the table. Watch the counters: two rows of the table can be one property.
PC lets the light through, survives the stone and keeps its shape in the sun. ABS wins only on cost and chemical resistance, and neither matters as much as seeing the road.
Pick four properties, write each one, then decide
Tap a row of the table to use it, then pick how you would write it. The page tells you which material each row favours, and when two rows are really one property. The checklist shows which marks your answer earns.
Your sentences appear here as you write them.
Five of five. Four properties, each compared between PC and ABS, and the decision in words with a reason that references transparency or impact strength.
Work through the model response one mark at a time
Try each mark yourself before you reveal it. Four marks are for properties compared from the table and one is for the decision.
PC is transparent with 88 to 90% light transmission, while ABS is opaque (0%), so only PC lets the rider see the road through the visor.
The sentence compares the transparency and light transmission of both materials. The two rows are one property, so using both in one sentence is the efficient way to earn this mark.
Each property must be compared between the two materials.
The Optical and Light transmission rows describe one property, and earn one mark between them.
Marker: describes properties from the table appropriately using wording indicating that PC is transparent (or has a high light transmission) while ABS is opaque
PC has a higher impact strength (600 to 850 J/m) than ABS (200 to 300 J/m), so a PC visor is less likely to crack or shatter when struck by stones or insects at speed.
It compares the impact strength values for both materials, then says why that matters for a visor. PC absorbs about three times the energy of ABS before it breaks. The Mechanical row (very high against high impact resistance) says the same thing in words, so it is the same property.
The Mechanical and Impact strength rows describe one property, and earn one mark between them.
Marker: describes properties from the table appropriately using wording indicating that PC has a higher impact strength than ABS
PC has a higher maximum service temperature (115 to 130 °C) than ABS (80 to 90 °C), so it is less likely to soften or distort when the helmet is left in the sun.
It compares the maximum service temperatures of both materials and links them to a helmet left in the sun. This is one of the three rows that can earn the third and fourth marks.
The third and fourth bullets may be awarded for any two of: maximum service temperature, chemical resistance, manufacturing cost.
Marker: describes properties from the table appropriately using wording indicating that PC has a higher maximum service temperature (better heat resistance) than ABS
ABS has a lower manufacturing cost than PC, but cost matters less than the rider’s vision and protection.
It concedes that ABS is cheaper, then judges cost less important for a visor. Naming a row that goes against your choice, and weighing it, shows you analysed the whole table. The Chemical row works the same way: ABS has better chemical resistance, but that matters less here.
Properties that favour ABS may be awarded marks as this shows the information in the table has been analysed.
Marker: describes properties from the table appropriately using wording indicating that ABS is cheaper than PC (or has better chemical resistance), but this is less important for this application
PC is the most suitable material for the visor because it is transparent and has the higher impact strength.
It chooses PC in words and cites transparency and impact strength. Choosing PC for heat resistance or dimensional stability alone does not earn this mark.
More properties favour PC. Therefore, the response must determine that PC is most suitable to be awarded the final mark.
Marker: determines that PC is the most suitable material for the visor, with a reason referencing transparency or impact strength
PC is transparent with 88 to 90% light transmission, while ABS is opaque (0%), so only PC lets the rider see the road through the visor. Mark 1 PC has a higher impact strength (600 to 850 J/m) than ABS (200 to 300 J/m), so a PC visor is less likely to crack or shatter when struck by stones or insects at speed. Mark 2 PC has a higher maximum service temperature (115 to 130 °C) than ABS (80 to 90 °C), so it is less likely to soften or distort when the helmet is left in the sun. Mark 3 ABS has a lower manufacturing cost than PC, but cost matters less than the rider’s vision and protection. Mark 4 PC is the most suitable material for the visor because it is transparent and has the higher impact strength. Mark 5
Each phrase of the question gave you something
If I had to guess where you might lose marks…
- Counting a pair of rows twice. You used the Optical and Light transmission rows (or the Mechanical and Impact strength rows) as two separate properties. Each pair earns only one mark, so you are one property short.
- Describing one material only. “PC is transparent” earns nothing on its own. Compare both: PC is transparent while ABS is opaque.
- Copying values without the visor. “PC is 600 to 850 J/m and ABS is 200 to 300 J/m” is a copy of the table. Say why it matters: a PC visor is less likely to crack when a stone hits it.
- The wrong reason for choosing PC. You chose PC with only heat resistance or dimensional stability as the reason. The decision mark needs a reason that references transparency or impact strength.
The past QCAA questions this one was modelled on
Only mark this done when you could do it without help. Reading the solution does not count.
A Tangent Tuition mock exam question. It is not a past QCAA question, and Tangent Tuition is not affiliated with the QCAA.
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